(1) Field of the Invention
The present invention relates to a radio frequency (RF) power amplifier used for amplifying power of an RF signal, and relates particularly to a multiband and multimode RF power amplifier which is compatible with different frequency bands and different wireless communication modes.
(2) Description of the Related Arts
To enable global utilization of a digital mobile terminal, a mobile terminal which is usable in a multiband frequency range (such as a range centering on 2 GHz and a range centering on 900 MHz) and a multimode system (such as Global System for Mobile Communications (GSM), Digital Communication System (DCS), and Universal Mobile Transmission Standard (UMTS)) is rapidly growing popular. Normally, in the configuration of a transmission power amplifier which amplifies a high-level output of electric power in the mobile terminal, a couple of semiconductor transistors for amplifying radio frequencies are connected in multiple stages. For compatibility with multiple bands and multiple modes, various power amplifiers and wireless communication devices using such power amplifiers have been considered (for example, see: Japanese Unexamined Patent Application Publication No. 2005-294894; Japanese Unexamined Patent Application Publication No. 2003-174111; U.S. Pat. No. 7,528,062 Specification; and Japanese Unexamined Patent Application Publication No. 2007-188916).
Generally, the power amplifier outputs a transmission power in a wide range of: approximately +35 dBm in GSM mode, approximately +33 dBm in DCS mode, and approximately +27 dBm to −50 dBm in UMTS mode. Particularly, near +35 dBm (GSM), +33 dBm (DCS), and +27 dBm (UMTS) where the power output within the mobile terminal is maximum, the influence on the receiving unit becomes maximum in the mobile terminal. Accordingly, it is necessary to suppress the influence to the receiving unit.
A power amplifier for the mobile device which is compatible with multiple bands and multiple modes has a configuration in which plural RF transmission circuits each including a power amplifier are connected in parallel so as to secure radio frequency characteristics. FIG. 7 shows a configuration of such a conventional RF power amplifier and a wireless communication device as described in Japanese Unexamined Patent Application Publication No. 2005-294894.
A wireless communication device 800 shown in FIG. 7 includes: a microphone 801; a speaker 806; an RF power amplifier 810; an antenna switch 813; an antenna 814; a Radio Frequency IC (RFIC) 815 which converts a baseband signal into an RF signal or converts an RF signal into a baseband signal; a baseband signal processing device 816; a duplexer 817a; filters 818a and 818b; matching circuits 820 and 821; a switch 830; filters 840b, 840c, 840d, and 840f; a gain control device 860; RF receiving circuit devices 8120 to 8122; and a transmission circuit 8130. Note that constituent elements enclosed by a dashed line constitute a first transmission path 8110, and a combination including filter 818a among a combination of constituent elements enclosed by an alternate long and short dash line constitutes a second transmission path 8111, and a combination including a filter 818b among a combination of constituent elements enclosed by an alternate long and short dash line constitutes a third transmission path 8112.
In this wireless communication device 800, the first transmission path 8110 including the duplexer 817a is used for communications in the UMTS mode (using, for example, 2 GHz band) in accordance with Code Division Multiple Access (CDMA) scheme; the third transmission path 8112 including the filter 818b and the second transmission path 8111 including the filter 818a are used, respectively, for communications in GSM mode (using, for example, 900 MHz band) and communications in Digital Communication System (DCS) mode (using, for example, 1.8 GHz band) in accordance with Time Division Multiple Access (TDMA) scheme.
In addition, downsizing and cost reduction is considered to be an important issue for the multiband and multimode mobile communications device, and in order to respond to this, in recent years, efforts have been made to share a single input path between frequency bands of two frequency ranges when the frequency bands of the RF signals supplied from RFIC 815 to the RF power amplifier 810 are relatively close to each other (such as frequency bands of 2 GHz and 1.8 GHz, and frequency bands of 850 MHz and 900 MHz).
For example, an approach of deleting, in FIG. 7, the filter 840c and sharing one input path for inputting the two RF signals from the RFIC 815 to the RF power amplifier 810 has been considered. In this case, although it is necessary to improve the performance of the RFIC 815, such a simplified interface between the RFIC 815 and the RF power amplifier 810 and the reduced number of terminals are expected to achieve improvements in size and costs. In other words, such a configuration can realize a wireless communication device which is compact, low cost, and capable of amplifying and transmitting electric power in response to multiple bands and multiple modes.